Alternating copolyestercarbonate resins

ABSTRACT

Alternating copolyestercarbonate resins having repeating units of the formula: ##STR1## wherein R 1  is para-phenylene; each R is independently an aromatic hydrocarbylene or inertly substituted aromatic hydrocarbylene, e.g., ##STR2## and x is a number from 0.05 to 0.65 exhibit physical properties such as heat resistance, clarity and impact strength that are superior to the comparable properties of corresponding random copolymers. Such resins are useful for making transparent tough films and molded articles having high heat resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of our copending applicationSer. No. 166,283, filed July 7, 1980 now U.S. Pat. No. 4,278,787, whichis a continuation-in-part of copending application Ser. No. 916,616,filed June 19, 1978, abandoned, which is a continuation-in-part ofapplication Ser. No. 795,978, filed May 11, 1977, now U.S. Pat. No.4,105,633.

BACKGROUND OF THE INVENTION

This invention relates to linear copolyesters that contain bothcarbonate groups and carboxylate groups in a linear chain.

Polycarbonate resins are known to be tough and rigid and have moderatelyhigh softening temperatures. Of particular interest are thepolycarbonates of bisphenol-A diols as described in U.S. Pat. No.3,028,365. On the other hand, polyesters such as those derived fromterephthalic acid, isophthalic acid and/or 1,4-butanediol are well knownas molding resins having high softening temperatures but poor impactresistances.

In the past, it has been a practice to make random linear copolymerscontaining ester and carbonate linkages in order to obtain polymershaving heat distortion temperatures generally higher than thosecharacteristic of polycarbonates. See, for example, U.S. Pat. Nos.3,169,121; 3,549,570; 3,053,810; 3,030,331 and 3,220,976. Unfortunately,however, the desired increase in heat distortion is often not as high asneeded for many applications. More importantly, any increase in heatdistortion is achieved only by sacrificing almost all of the high impactresistance that is characteristic of polycarbonate resins.

In view of the aforementioned deficiencies of conventional polyesters,polycarbonates and copolymers thereof, it would be highly desirable toprovide a polymer of the same or similar monomeric materials whereinimproved heat resistance is obtained without almost total sacrifice ofimpact resistance.

SUMMARY OF THE INVENTION

Accordingly, the present invention is such a polymer. This polymer is anormally solid alternating copolyestercarbonate having repeating unitsof the formula: ##STR3## wherein each R is independently aromatichydrocarbylene or inertly substituted aromatic hydrocarbylene, R¹ ispara-phenylene or inertly substituted para-phenylene and x is a numberfrom 0.05 to 0.65, preferably from 0.05 to 0.58. For the purposes ofthis invention, an "inertly substituted" group is one having one or moresubstituents which are inert in the condensation reaction used toprepare the copolymer. "Hydrocarbylene" is a predominantly hydrocarbondivalent radical including aliphatic and/or aromatic hydrocarbondiradicals as well as hydrocarbon radicals linked together by ##STR4##

This alternating copolymer is advantageously prepared by first reactingan excess of a dihydric hydrocarbylene with a terephthaloyl halide andthen reacting the resulting dihydroxyester product with phosgene or asimilar compound capable of forming carbonate linkages with diols. Thefirst reaction is advantageously carried out in the presence of ahydrogen chloride acceptor such as pyridine. The second reaction istypically effected using conditions common to the reaction of phosgenewith simple diols to form polycarbonates. This two-step reaction toprepare the alternating coplymer can be represented by the following:##STR5## wherein R, R¹ and x are as defined hereinbefore.

While the alternating copolymers of this invention are similar in manyrespects to their corresponding random copolymers, they exhibit heatresistance, clarity, solubility and strength that are unexpectedlyhigher than those of the random copolymers. Even more surprising is thatsuch alternating copolymers exhibit impact strength (at 23° to -30° C.),notch sensitivity and processability that are unexpectedly superior tothe same properties of alternating copolymers that are similar in allrespects except that x is from about 0.67 to about 1.86. Further, thealternating copolymers of this invention exhibit notch sensitivity, lowtemperature impact strength (at 0° to -30° C.), heat resistance andresistance to embrittlement following heat aging that are unexpectedlysuperior to the same properties of bisphenol-A polycarbonate.Accordingly, the alternating copolymers of this invention, particularlythe resinous ones, are useful in most applications in whichpolycarbonates, polyesters and copolymers thereof are conventionallyemployed. In particular, such alternating copolymers are useful formaking transparent tough films and molded articles having high heatresistance. In addition, such alternating copolymers may be blended withother polymers such as ABS resins, styrene/acrylonitrile copolymers andimpact polystyrenes to provide molding blends and/or they may becombined with reinforcing fibers such as glass fibers.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The dihydric hydrocarbylene employed in preparing the copolymers of thisinvention is suitably any predominantly hydrocarbon compound containingat least two alcoholic hydroxyl groups wherein alcoholic hydroxylincludes phenolic hydroxyl. Included within the dihydric hydrocarbylenesare aliphatic diols including glycols and cycloaliphatic diols, aromaticdiols, including alkaryl diols, dihydric phenols and aromatic diolshaving heterocyclic groups such as phenolphthalein. Of the dihydrichydrocarbylenes, the dihydric phenols are preferred.

The dihydric phenols preferably used in preparing the alternatingcopolymers of the present invention are suitably any aromatic compoundhaving an aromatic hydrocarbylene group to which is aromatically bondedtwo hydroxyl groups. Most advantageously, the dihydric phenols are thosearomatic diols represented by the formula: ##STR6## In the formula, A isan aromatic group such as phenylene, biphenylene, naphthenylene,anthracenylene and the like. E is alkylene or alkylidene such asmethylene, ethylene, ethylidene, propylene, propylidene, isopropylidene,butylene, butylidene, isobutylidene, amylene, isoamylene, amylidene andisoamylidene or E may be cycloalkylene such as cyclopentylene,cyclohexylene; a sulfur-containing linkage such as sulfide, sulfoxide orsulfone, an ether linkage; a carbonyl group; a tertiary nitrogen groupor a silicone-containing linkage such as silane or siloxy. R is hydrogenor a monovalent hydrocarbon group such as alkyl, aryl, arylalkyl orcycloaliphatic; Y is chlorine, bromine, fluorine or R wherein R is asdefined above. The letter m is any whole number from and including zerothrough the number of positions on A available for substitution; p isany whole number from and including zero through the number of availablepositions on E; t is a whole number equal to at least one; s is eitherzero or one; and u is any whole number including zero. Examples of suchdihydric phenols include 2,2-bis-(4-hydroxyphenyl)propane [bisphenol-A],bis-(4-hydroxyphenyl)methane, 1,1-bis-(4-hydroxyphenyl)ethane and othersincluding dihydroxy aromatic ethers listed in U.S. Pat. No. 3,169,121 atColumn 2, line 60 through Column 3, line 55.

Also included among the suitable dihydric phenols are those having anar,ar'-dihydroxytrityl nucleus represented by the formula: ##STR7##wherein the aromatic rings bear, in addition to the hydroxysubstituents, such substituents as H, F, Cl, Br, I, --NO₂, --O--, alkyl,acyl, carboxylate ester, sulfonate ester and the like. Representativediols containing the ar,ar'-dihydroxytrityl nucleus includephenolphthalein nucleus compounds as described in U.S. Pat. No.3,036,036; phenolsulfonephthalein nucleus compounds described in U.S.Pat. No. 3,036,037; phthalidene nucleus compounds as described in U.S.Pat. No. 3,036,038; fluorescein nucleus compounds as described in U.S.Pat. No. 3,036,039; and phenolphthalimidene nucleus compoundscorresponding to the phenolphthalein nucleus compounds described in U.S.Pat. No. 3,036,036; all of which patents are hereby incorporated byreference. Of the aforementioned dihydric phenols, thebis(ar-hydroxyphenyl)alkylidenes, particularly bisphenol-A, andphenolphthalein are preferred, with bisphenol-A being most preferred.

In the preparation of the alternating copolymers of this invention, anyterephthaloyl halide is suitably employed. Most preferably, however, theterephthaloyl halide is terephthaloyl chloride, with terephthaloylbromide and terephthaloyl iodide being suitable but less preferred thanthe chloride. Suitable alternatives to the terephthaloyl halide includeinertly substituted derivatives of terephthaloyl halide wherein an inertsubstituent is halo, hydrocarbyl such as alkyl or aryl, halohydrocarbyland the like. The terephthaloyl halides are prepared by reacting thedesired terephthalic acid with thionyl chloride or other thionyl halidein aromatic solvent, e.g., under conditions described in High Polymers,Vol. XXVII, "Condensation Monomers," J. K. Stille and T. W. Campbell,editors, pages 509-514, Wiley-Interscience, 1972. Exemplary diacidsinclude terephthalic acid and halo derivatives thereof.

The alternating copolymers are advantageously prepared by a two-stepprocess wherein an excess of the dihydric hydrocarbylene is firstreacted with the terephthaloyl halide in the presence of a hydrogenchloride acceptor such as pyridine. The dihydroxyester intermediateproduced by this reaction is then reacted with phosgene or other agentwhich will suitably form the desired carbonate linkages. Both steps ofthe process are normally carried out under an inert atmosphere such asnitrogen with the reactants dissolved in one or more solvent such thatthe reactants are totally miscible. While the concentrations of thereactants in the solvents are not particularly critical, theconcentration of dihydric hydrocarbylene is preferably from about 2 toabout 10 weight percent and the concentration of the terephthaloylhalide is preferably from about 1 to about 5 weight percent based on thetotal weight of monomers and solvents. In the second step of thereaction, the concentration of ester intermediate is preferably fromabout 3 to about 15 weight percent based on total weight of esterintermediate and solvents. It is preferred that the solutions of thevarious reactants be totally miscible in each other. It is sufficient,however, if such solutions are partially miscible, i.e., at least 10weight percent. Examples of suitable solvents include chlorinatedaliphatic hydrocarbons such as methylene chloride, chloroform,sym-tetrachloroethane, 1,1,2-trichloroethane andcis-1,2-dichloroethylene.

The molar ratio of dihydric hydrocarbylene to terephthaloyl halidevaries proportionately with the ester:carbonate ratio desired in thealternating copolymer. Generally, the molar ratio of dihydrichydrocarbylene to terephthaloyl halide is advantageously from about 21:1to about 2.5:1, preferably from about 21:1 to about 2.9:1. The molarratio of dihydroxyester intermediate to phosgene is advantageously fromabout 1:1 to about 1:1.2, preferably about 1:1.01 to about 1:1.08.

While pyridine is the preferred hydrogen chloride acceptor employed inthe first step of this process, other suitable acceptors include otheramine bases such as triethylamine, N,N-dimethylaniline andN,N-dimethylcyclohexylamine. Such acceptors are advantageously employedin amounts sufficient to complex the hydrogen chloride liberated and tocatalyze both steps of the process.

Since higher concentrations of the acceptor produce higher molecularweight copolymers, actual concentrations of acceptor will vary dependingupon the molecular weight desired. Moreover, at constant terminatorlevels, higher monomer concentrations produce higher molecular weightcopolymers. Therefore, the concentrations of monomers vary dependingupon the molecular weight desired. Preferably, in order to preparecopolymers having weight average molecular weights (Mw) from 25,000 to60,000, the acceptor is employed in amounts from about 100 to about 160mole percent based on moles of hydroxyl moiety in the monomers, mostpreferably from about 120 to about 140 mole percent. At such acceptorconcentrations, the concentrations of monomers are preferably in therange from about 3 to about 15 weight percent, most preferably fromabout 5 to about 12 weight percent.

In carrying out the two-step process, the dihydric hydrocarbylene andterephthaloyl halide are combined in any manner, preferably by addingthe terephthaloyl halide either neat or dissolved in a suitable solventwith stirring to a solution of the dihydric hydrocarbylene and hydrogenchloride acceptor. While stirring rate is not critical, a stirring rateof about 50 to about 500 rpm, most preferably from about 150 to 300 rpm,is maintained. While reaction temperature is not critical, the reactiontemperature of the first step is preferably maintained in the range fromabout 10° to about 35° C., most preferably from about 19° to about 25°C. Reaction pressures are similarly not critical, however, atmosphericto superatmospheric pressures are normally employed as a matter ofconveniene. The ester intermediate is normally formed under theseconditions in about 1 to about 10 minutes after addition of theterephthaloyl halide. While the ester intermediate may be recovered andpurified before proceeding to the second step of the process, it isgenerally not desirable to do so.

Accordingly, the aforementioned reaction mixture containing the esterintermediate is converted to the desired copolymer by bubbling phosgeneor other suitable carbonate forming reactant into the reaction mixture.Advantageously, the reaction mixture contains an amount of a monohydricphenol or other suitable chain terminator to effect desired control ofthe molecular weight of the resulting copolymer. While the amount ofchain terminator employed varies with the efficacy of the terminator andthe molecular weight desired, beneficial amounts of terminator arenormally in the range from about 1 to about 10 mole percent based onester intermediate, preferably from about 2 to about 7 mole percent.Although not critical, the reaction temperature of the second step ispreferably maintained in the range from about 10° to about 35° C., mostpreferably from about 20° to about 27° C. As in the first step, reactionpressures are normally atmospheric to superatmospheric as a matter ofconvenience. The alternating copolymer is normally formed under theseconditions in about 1 to about 10 minutes after phosgene addition.

In both steps of the foregoing process, the reaction mixture is agitatedsufficiently to effect intimate contact of the reactants and desiredheat transfer throughout the reaction medium. Following completion ofthe second step of the process, the desired alternating copolymer isreadily recovered from the reaction medium by conventional techniques asexemplified in the following examples. Due to the ease of preparationand less expensive starting materials, the alternating copolymersderived from bisphenol-A and terephthaloyl chloride are preferred.

The alternating copolymers of this invention are more advantageouslyrepresented by the formula: ##STR8## wherein Y and Z are independentlyterminating groups common to polyesters or polycarbonates; R, R¹, and xare as defined hereinbefore and n is a whole number from about 5 toabout 300. Illustratively, Y is ##STR9## wherein R² is hydrocarbyl suchas alkyl, aryl or aralkyl; and R and R¹ are as defined hereinbefore.Representative Z includes

    R.sup.2 -- and HOR--

wherein R² and R are as defined hereinbefore.

The alternating copolymers having repeating units are mostadvantageously represented by the formula: ##STR10## wherein Y is --OHor ##STR11## Z is --R² or --ROH; x is preferably 0.05 to 0.58, mostpreferably 0.056 to 0.52; and R, R¹, R² and n are as definedhereinbefore. Preferred alternating copolymers are those represented bythe foregoing formula wherein Y is ##STR12## Z is --R² ; R² ishydrocarbyl, e.g., alkyl, aryl, alkaryl, cycloalkyl or aralkyl; and n isa whole number from about 5 to about 300, preferably from about 10 toabout 200 and most preferably from about 30 to about 150. For purposesof this invention, hydrocarbyl is a monovalent hydrocarbon radical. Inthe most preferred alternating copolymers Y is ##STR13## Z is --R² ; R²is ##STR14## R is ##STR15## and R¹ is ##STR16##

While the molecular weight of the alternating copolymers of thisinvention is not particularly critical, those having weight averagemolecular weight (Mw, determined by gel permeation chromatography usinga bisphenol-A polycarbonate calibration curve) greater than 20,000 areof more significance. It is found that those copolymers of relativelyhigh molecular weight, e.g., those having a Mw of at least about 25,000up to and including those having a Mw of about 60,000, are found toexhibit the properties and physical characteristics most desirable ofmolding resins. Most preferred for this purpose are those copolymershaving a Mw in the range from about 25,000 to about 40,000 and Mw/Mn(number average molecular weight) from about 1.5 to about 5.

The following examples are given to illustrate the invention and shouldnot be construed as limiting its scope. Unless otherwise indicated, allparts and percentages are by weight.

EXAMPLE 1 Preparation of the Alternating Copolymers

In step one of a two-step process, a 12-l (liter) flask is charged with893 g (3.91 mol) of bisphenol-A, 8.0 l methylene chloride and 804.3 g(10.2 mol) pyridine. Stirring is begun and when a clear solution ofbisphenol-A is obtained, 41.8 g (0.21 mol) terephthaloyl chloride isadded continuously over a period of 2 minutes while continuouslystirring the contents of the flask at 22° C. and 250 rpm. The clearreaction solution is stirred an additional 10 minutes followingterephthaloyl chloride addition before the second step of the process isbegun.

In step two, the aforementioned reaction solution containing the esterintermediate is combined with 13.9 g (0.093 mol) p-tert-butylphenol (aschain terminator). The resulting solution is stirred at 175 rpm and 396g (4.0 mol) phosgene is added over a period of 135 minutes by bubblingthe phosgene into the liquid reaction solution at 19°-26° C.

The resulting polymeric product is recovered from the reaction mixtureby the following procedure: 1.75 l of 3.0 N HCl is added to neutralizeexcess pyridine. Following phase separation, the methylene chloridesolution of polymer is washed consecutively with 1.0 l of 0.5 N HCl and1.0 l of water, with phase separation after each washing. Following thefinal washing, the methylene chloride solution of polymer is passedthrough a column packed with a cation exchange resin (sulfonic acidtype, bed volume of 500-600 ml), giving a clear, almost water-whitesolution. The polymeric product is isolated by the slow addition of 1volume of methylene chloride solution to 4 volumes of hexane with rapidstirring. The resulting white fibers are isolated by filtration, driedin air for 24 hours and then dried in vacuo 48 hours at 120° C. to yield913.3 g (89.9 percent of theory) having an inherent viscosity of about0.49 dl/g (measured in methylene chloride at 25° C., 0.5 g/dl).

Analysis of the polymer by IR, NMR and elemental analysis indicates thatit is an alternating copolymer represented by the structural formula:##STR17## The copolymer repeating unit has an ester:carbonate ratio of0.11:1.

This copolymer (Sample No. 1) is injection molded using a Newbury Hl30RS machine equipped with a Control Process, Inc. Process Sentry Model750 and Process Recorder. The following molding conditions are used:barrel zones--316° C., nozzle--304° C., mold halves--121° C., injectiontime--10 seconds, total cycle time--45 seconds, feed setting--2.5,tensile bar and runner limits--2,000 psi and single stage injectionmode. To determine processability of the polymer, the injection pressurerequired to obtain a pressure of 4,000 psi at the end of the moldedtensile bar is measured. The physical properties and processabilitymeasurements for the 0.32 cm thick injection molded specimens are shownin Table I.

Following the general procedure of this example, copolymers are preparedusing bisphenol A, terephthaloyl chloride and phosgene withester:carbonate ratios of 0.33:1 (Sample No. 2), 0.67:1 (Sample No. 3)and 1:1 (Sample No. 4). These copolymers are injection molded asdescribed hereinbefore and the physical properties and processabilityresults for the 0.32 cm thick injection molded specimens are shown inTable I.

For purposes of comparison, a commercial bisphenol A polycarbonate,Merlon M-50F sold by Mobay Chemical Corp. (Sample No. A) and a copolymerprepared using bisphenol A, terephthaloyl chloride and phosgene with anester:carbonate ratio of 2:1 (Sample No. B, prepared using the generalprocedure of this example) are injection molded as describedhereinbefore. Physical properties and processability results for the0.32 cm thick injection molded specimens are shown in Table I.

                                      TABLE I                                     __________________________________________________________________________               Sample No.                                                                    A*  1   2     3   4   B*                                           __________________________________________________________________________    E:C (1)    0:1 0.11:1                                                                            0.33:1                                                                              0.67:1                                                                            1:1 2:1                                          Inherent viscosity                                                            (2), dl/g  0.50                                                                              0.49                                                                              0.54  0.51                                                                              0.56                                                                              0.55                                         M.sub.w (3)                                                                              54,963                                                                            54,740                                                                            59,919                                                                              51,932                                                                            57,647                                                                            55,162                                       M.sub.w /M.sub.n (3)                                                                     2.45                                                                              2.27                                                                              1.97  1.98                                                                              2.00                                                                              1.80                                         Vicat softening                                                               (4), °C.                                                                          157 161 172   177 184 197                                          Injection pressure                                                            (5), psi   5,000                                                                             5,000                                                                             7,500 7,750                                                                             12,500                                                                            16,000                                       Tensile at yield                                                              (6), psi   8,548                                                                             8,653                                                                             8,705 8,653                                                                             8,766                                                                             9,012                                        Tensile at break                                                              (6), psi   7,326                                                                             8,264                                                                             8,969 8,109                                                                             8,441                                                                             8,480                                        Elongation at yield                                                           (6), %     6.08                                                                              6.37                                                                              6.85  7.35                                                                              7.52                                                                              8.47                                         Elongation at break                                                           (6), %     121.0                                                                             94.8                                                                              80.2  69.0                                                                              49.0                                                                              34.5                                         Tensile modulus                                                               (6), psi   301,000                                                                           330,000                                                                           315,000                                                                             300,000                                                                           295,000                                                                           308,000                                      Izod impact (7),                                                              ft-lb/in, notched                                                               23° C. (8)                                                                      15.5                                                                              13.1                                                                              11.8  9.2 8.6 6.0                                            23° C. (9)                                                                      2.2 13.0                                                                              11.3  8.5 7.4 4.8                                             0° C. (8)                                                                      11.0                                                                              13.1                                                                              Not Meas.                                                                           9.8 7.6 5.5                                           -18° C. (8)                                                                      4.8 13.0                                                                              11.3  7.9 6.0 5.1                                            -30° C. (8)                                                                     3.0 8.1 9.2   5.7 5.7 5.5                                          Transmission (10), %                                                                     89.1                                                                              86.3                                                                              87.1  88.1                                                                              86.6                                                                              84.5                                         Haze (10), %                                                                             2.0 1.8 2.5   2.1 3.2 4.5                                          Yellowness Index (11)                                                                    3.3 6.7 5.4   5.9 9.0 10.3                                         __________________________________________________________________________     *Not an example of the invention                                              (1) Mole ratio of ester:carbonate in copolymer.                               (2) Measured in CH.sub.2 Cl.sub.2 at 25° C., 0.5 g/dl.                 (3) M.sub.w  weight average molecular weight, M.sub.n  number average         molecular weight, both determined by gel permeation chromatography using      polystyrene calibration.                                                      (4) ASTMD-1525.                                                               (5) Pressure required to obtain 4,000 psi at end of tensile bar.              (6) ASTMD-638.                                                                (7) ASTMD-256.                                                                (8) 0.254 mm notch radius.                                                    (9) 0.127 mm notch radius.                                                    (10) ASTMD-1003.                                                              (11) ASTMD-1925.                                                         

As evidenced by the data set forth in Table I, the alternatingterephthalate copolymers of this invention exhibit physical properties,particularly impact strength (at 23° C. to -30° C.), notch sensitivityand processability, that are generally superior to the same propertiesof the alternating terephthalate copolymer with an ester:carbonate ratioof 2:1. In addition, they exhibit physical properties, particularlynotch sensitivity, low temperature impact strength (at 0° C. to -30°C.), heat resistance and tensile strength, which are generally superiorto the same properties of bisphenol A polycarbonate.

EXAMPLE 2

Following the general procedure of Example 1, other copolymers areprepared using terephthaloyl chloride, phosgene and aromatic diols asspecified in Table II. These copolymers, which have an ester:carbonateratio of 1:1, are compression molded at 300° to 330° C. and tested forphysical properties as recorded in Table II. The copolymers aretransparent when molded.

                  TABLE II                                                        ______________________________________                                               Sample No.                                                                    5     6           7           8                                        ______________________________________                                        Aromatic                                                                      diol (1) BA      BA/PP       BA/PP     PP                                     (molar ratio)                                                                          (1.00)  (0.58/0.42) (0.50/0.50)                                                                             (1.00)                                 Inherent                                                                      viscosity                                                                     (2), dl/g                                                                              0.55    0.52        0.62      0.58                                   M.sub.w (3)                                                                            57,296  60,076      66,258    53,734                                 M.sub.w /M.sub.n (3)                                                                   1.93    1.69        2.76      2.27                                   Tg (4), °C.                                                                     172     219         212       276                                    Izod impact                                                                   (5), ft-lb/in.                                                                notched  8.5     3.6         3.7       1.1                                    Tensile at                                                                    yield (6), psi                                                                         8,800   11,497      Not measured                                                                            (8)                                    Tensile at                                                                    break (6), psi                                                                         8,500   10,355      "         11,358                                 Elongation at                                                                 yield (6), %                                                                           7.6     8.8         "         (8)                                    Elongation at                                                                 break (6), %                                                                           40      14          "         5                                      Tensile mod-                                                                  ulus (6), psi                                                                          300,000 350,000     "         362,000                                Oxygen index                                                                  (7), % O.sub.2                                                                         30      Not measured                                                                              "         44                                     ______________________________________                                         (1) BA = bisphenol A, PP = phenolphthalein.                                   (2) Measured in CH.sub.2 Cl.sub.2 at 25° C., 0.5 g/dl.                 (3) M.sub.w  weight average molecular weight, M.sub.n  number average         molecular weight, GPC, polystyrene calibration.                               (4) Glass transition temperature, determined by DSC.                          (5) ASTMD-256.                                                                (6) ASTMD-638.                                                                (7) ASTMD-2863.                                                               (8) Sample did not exhibit a yield point.                                

EXAMPLE 3

Following the general procedure of Example 1, a copolymer is preparedusing bisphenol A, terephthaloyl chloride and phosgene with anester:carbonate ratio of 1:1 and an inherent viscosity of about 0.60dl/g (measured in methylene chloride at 25° C., 0.5 g/dl). Injectionmolded test bars of this copolymer (Sample No. 9) are prepared asdescribed hereinbefore with a thickness of 0.32 cm.

For purposes of comparison, the commercial bisphenol A polycarbonate(Sample No. A) used in Example 1 is injection molded as describedhereinbefore to give 0.32 cm thick test bars. Standard ASTM-D-256notched Izod impact specimens with a 0.254 mm notch radius are machinedfrom the injection molded test bars of Sample No. 9 and Sample No. A.These specimens are placed in an oven at 120° C. and the effect of heataging on notched Izod impact strength is determined as recorded in TableIII.

                  TABLE III                                                       ______________________________________                                                     Sample No. A*                                                                           Sample No. 9                                           ______________________________________                                        E:C (1)        0:1         1:1                                                Izod impact (2), ft-lb/in,                                                    notched                                                                        As molded     18.2        7.9                                                 2 days at 120° C.                                                                    6.2         6.4                                                 4 days at 120° C.                                                                    2.5         6.6                                                 16 days at 120° C.                                                                   2.0         6.9                                                 32 days at 120° C.                                                                   1.6         5.5                                                 64 days at 120° C.                                                                   1.6         5.6                                                ______________________________________                                         *Not an example of the invention.                                             (1) Molar ratio of ester:carbonate in copolymer.                              (2) ASTMD-256.                                                           

As evidenced by the data set forth in Table III, the alternatingterephthalate copolymers of this invention exhibit resistance toembrittlement following heat aging which is generally superior to thesame property of bisphenol A polycarbonate.

What is claimed is:
 1. A normally solid alternating copolyestercarbonatehaving repeating units of the formula: ##STR18## wherein each R isindependently an aromatic hydrocarbylene or inertly substituted aromatichydrocarbylene, R¹ is para-phenylene or inertly substitutedpara-phenylene and x is a number from 0.05 to 0.52.
 2. Thecopolyestercarbonate of claim 1 wherein x is a number from 0.056 to0.52.
 3. The copolyestercarbonate of claim 1 or 2 represented by theformula: ##STR19## wherein each R is independently aromatichydrocarbylene or inertly substituted aromatic hydrocarbylene, R¹ ispara-phenylene; Y is --OH or ##STR20## Z is --R² or --ROH; R² ishydrocarbyl and n is a whole number from about 5 to about
 300. 4. Thecopolyestercarbonate of claim 1 wherein each R is ##STR21## and each R¹is ##STR22##